neigh: Protect neigh->ha[] with a seqlock

Add a seqlock in struct neighbour to protect neigh->ha[], and avoid
dirtying neighbour in stress situation (many different flows / dsts)

Dirtying takes place because of read_lock(&n->lock) and n->used writes.

Switching to a seqlock, and writing n->used only on jiffies changes
permits less dirtying.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 4 deletions

diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index f35309578170..d8e540c5b071 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -502,10 +502,8 @@ int arp_find(unsigned char *haddr, struct sk_buff *skb)
 
         if (n) {
                 n->used = jiffies;
-                if (n->nud_state&NUD_VALID || neigh_event_send(n, skb) == 0) {
-                        read_lock_bh(&n->lock);
-                        memcpy(haddr, n->ha, dev->addr_len);
-                        read_unlock_bh(&n->lock);
+                if (n->nud_state & NUD_VALID || neigh_event_send(n, skb) == 0) {
+                        neigh_ha_snapshot(haddr, n, dev);
                         neigh_release(n);
                         return 0;
                 }